System of x-ray-tube operation.



GLR. HOGAN & H. P. MACLAGAN. SYSTEM OF X-RAY TUBE OPERATION.

APPLICATION FILED APR. I3. I9I4.

Patented J an. 30, 1917.

Z AIRIllll UNIT D STATES PATEn r on.

GEORGE R. HOGAN AND HECTOR P. MACLAGAN, OF CI'HGAGC, ILLiNOIS,

SYSTEM OF X-RAY-TUBE OPERATION.

Application filed April 13, 1914.

To all whom it may concern:

Be it known that we, GEORGE R. HOGAN and Hno'ron P. MACLAGAN, citizens of the inited States, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Systems of X-Ray-Tube Operation, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

Our invention relates to an improved system of X-ray tube operation by which a more intense X-ray field is produced with simpler apparatus than has heretofore been possible in'the art.

Our invention is characterized by the use Y of such a voltage of alternating current impressed directly upon the terminals of an X-ray tube that the current will flow in one direction through the tube, whereas it will not flow in the other direction. Or in other words, the properties of the tube are such that half of the waves of the high tension alternating current impressed upon the terminals of the tube are suppressed within the tube itself.

Heretofore in the art it has been customary to excite X-ray tubes in several ways. One of the earliest systems employed involved the use of a static machine for gencrating the high tension current delivered to the X-ray tube. Subsequently high tension induction coils were employed for this purpose with the result, however, that it was almost, it not quite, impossible to prevent the fiow through the X-ray tube of current rays in the reverse of the desired direction with the accompanying production of the so-called inverse waves in the tube, which produced a character of illumination preventing the proper use of the tubes. It has always been found that the production of these inverse waves results in an illumination due to a more or less pronounced disruptive arcing within the tube between its ternnnals, and the production of sucli arcs makes it impossible at the same time to produce in the tube the X-rays which are required for radiographic purposes. The ideal character of illumination in the tube for radiographic pur; uses is one resulting from a quiet discl'iarge in but one direction through the tube, which produces a yellow greenish illumination upon one side only of thetarget of the tube, a re Specification of Letters Patent.

,rent supply is an alternating current or Patented Jan, 30., 191% Serial No. 831,372.

sult of which, for ideal conditions there is a pronounced hemisphere of illun'iination with practically an entire absence of illuini nation in the other half of the tube. It gll been found to be practically impossible to secure this character of illumination with the induction. coil system of operation.

The systems more recently used, wi much better results, are of two kinds; the high frequency system, in which called Tesla coils are used; and transformer system in which a recti ing switch of one kind or another, equivalent rectifying devices are employed so in the high tension circuit connecting with the tube. in the former of these syster u, the tube is connected directly with the minals of the secondary winding of transformer but it is found necessary invariably use in this system an tuho provided with a so-called valve for pressing the inverse waves which would otherwise be produced in the tube. The primary winding oi? the transformer in such a system may be operated either by direct current or by alternating current, but in any event an interrupter is used, the terminals of which have connected around thorn a condenser of large capacity, as a result of which a high frequency oscillatory discharge is produced through the primary windi of the transformer, and thus a high ti quency high tension current is deii from the terminals of the secondary w oing of the transformer to the X-ray tube. The transformers used in this system. not equipped with magnetic core for the reason that the high frequency of operat prevents an eli'cctive and etlicient transfon mation of the cin'rent. The transformer system of operation consists in using a high tension step-up transformer, the prii'nary winding of which is supplied directly with alternating current produced either by rotary converter when the source oi. cur-- the alternating current generator of a motor generator set when the source of motor s ply is a direct current. In connectu this system of operation it is customary to provide a i'ectitving switch mounted :upon the sha '1- of the rotary converts motor genera that the switch operate a l i; icrtcct s; with the she I this rec l yi .5-

i with .circuit extending from the secondary wind;

ing of the transformer so as to deliver these high tension impulses to the Iii-ray tubes always in the same direction. Various mochiications of this co-callcd transformer systom hath been proposed, such for. example as substituting for the rectifying switch rectifying devices of other descriptions 1n the secondary circuit.

lln every case of -iii-ray tube operation as far as We are aware, with the exception oi systems in which valve tubes are employed, it has been found necessary to deliver to the terminals oi the X-ra y tube a uni-directional current, for. otherwise it has been found that inverse Waves are produced in the tubes By our present invention We are able to connect the terminals of the high tension secondary Winding of the transformer directly with the terminals of the X-ray tube without the use of rectifying devices of any kind or description. That is to say,'we in;- press upon the terminals of the tube an alternating high tension electromotive force, and yet by the particular relation of that electromotive force to the constants oi the tale We produce a uni-directional ilow of current through the tube. li e are not entirely informed as to Why this result is produced, but our experiments thus far indicate that the resistance of the tube from the target to the mirror or cathode is less than the rgsistance from the mirror to the target, for We find that reversing the connections of the secondary Winding to the terminals of the tube merely changes the direction of current flow in said Winding without producing any change \vl'iatcver in the character of operation of the tube and, further-- more, for either connection current flowing through .the secondary circuit is uni-directional. It will be understood that in our improved system we employ ordinary high tension X-ray tubes without valves and that therefore, the entire effect of suppressing the high tension alternating current Waves of one sign is produced by the target and cathode in some manner.

From results secured by oursystem We conclude that every X-ray tube has a critical value of operating elcctromotive force which if impressed upon the terminals oil the tube, even though the electromotive force be alternating in character, will produce a uni-current flow through the tube, whereas if the potential impressed upon. the terminals be increased somewhat the ilow ot' current through the tube becomes alternating in.

nection vwith but one embodiient of our rent motive force to produce a brush the charge from the target to the cathode and maintaining the said elcctroinotive t'orce at a value too low to produce a disruptive alter; hating discharge between target and cathode for We iind there is distinctly ao preciablc range of o 'icration of vari X-ray tubes, each having characteristic range, through which a uni-directioinil rush discharge may be produced by a high tensio l alternating electroinotive :lorce 0:5 proper value without the production oi an altei ing disruptive discharge, and that for range of operation a practica ly per'l'et hemispherical illumination resulting the cathode rays reflected by the in upon the target is produced.

in carrying out our invention we l advisable to use a tra'ns'lio nor hav A closed magnetic path, since ti o ciiicie-ncy of tltUlS'fOl'll'lilt lOZ is relatively ligh by means of such device.

The several drawings illustrating our invention are as follows:

l inure l is a dizugrainunitic view showing our system in its complete embed.invent cur-- rent being supplied to ti o ill be by means of a rotary converter; i2 sl ous in a similar diagramniatic view our system op rated by means oi a motor gcncratm shows in a view sii In to Fig. l. our sy operated by means oi alternating curr supplied to the transform 1 directly the line; Fig. 4-. is a detail view of the trans former used in connection with our system.

Similar numerals refer to similar parts throughout the several views.

.llh carryingout our invention it is immatcr'al in what manner the primary Windin; oi the transformer is excited as long as an alterating; current of proper potential and current strength is delivered to the pri mary Winding oi said transformer. The operation of the system inany event is pre cisely the same so that it will be necessary to describe the operation in detail in tern, for example that shown in Fig. 1. primary winding: i, of the transformer supplied with altcrnatinn current i i-on rotary converter 3, which rotary Lconverter is driven by direct current supplied by th main feed wires 4 2 nd 5. llith this sysii the potential oi the current deliver -d to the primary Winding l olf course subs" in tially the same as the potential between main feed Wires l and/5. la the sys shown in l 2, on the'iothcri hand the pi. inary wini up; 1 of the transformer 93 supplied with alternating. current "from the alternating); current generator ll. of the motor generator 7 the motor clcn'icnt 8 oil which is driven by direct current sup} main f ed Wires 9 and i0. bodiinent of our system of course, .oe l j understood that the electromotive force delivered by the alternating current generator 6 may have any desired relation to the electromotive force between the direct current feed wires 9 and 10.

In the embodiment of our system shown in Fig. 3, the alternating current is supplied to the primary winding 1 of the transformer 2, either by means of a transformer 11 supplied with alternating current directly from the line wires 12 and 13 or if the alternating voltage between the line wires 12 and 13 is of the proper value, the line wires may be connected directly with the terminals of the primary "winding 1".

The differences described are the only ones existing in the operation of the various embodiments of our system disclosed, and any one of these systems of operation will properly energize the transformer so as to deliver the desired alternating high tension current from the secondary winding of said transformer. To consider the further operation of our system, therefore, it will be necessary to describe but one embodiment of our system, as for example, that shown in Fig. 1. I

As a result of the excitation of the core of the transformer 2, by the alternating current flowing through the primary winding 1, a high tension electromotive l'w'ce is developed in the secondary winding 14 of the transformer 2, of a proper voltage to carry out our system in connection with the tube 15. The terminals of the secondary winding 14 are connected by conductors 10 and 17 with the terminals 18 and 10 respectively of the tube 15. The terminal 18 is connected by a rod 20, preferably with a copper cylinder 21 having its inner end beveled at substantially degrees, and provided. with a central circular target pre'l'eral'ily of tungsten. The other terminal 10 is connected by a rod 23 with a concave mirror 24 facing the beveled end of the cylinder 21. The mirror is made preferably oi, aluminum, and in all respects the tube 15 is of standard construction, designed for use in connection with high tension operation, by means of a rec tit'ying or transtorn'iing switch. The alternating electronmtive 'lorce developed by the secondary winding 14 is sull'icient when impressed upon the cylinder 21 and mirror 2% to cause a brush discharge or non-arcing current ilow from the cylinder to the mirror as indicated. This high tension electromotive force is not suiiicient, however, to ca use a current flow of any description from the mirror to the cylinder. as a result of which, the current flowing through the tube is unidirectional and pulsating. the efl'ect being to utilize the entire energy represented by all of the high tension electromotive force 'avcs of one sign with the greatest efif at the same time the effect upon the alternating high tension waves of opposite sign is: substantially the same as though at the particular instance of the occurrence of these waves of opposite sign the secondary circuit of the transformer 2 were open. Our experiments have shown, conclusively, that with the same high tension alternating elec tromotive force developed by the secondary winding 14, when this electromotive force is sufiicient to produce a brush discharge from the cylinder 21 to the lnirror 24, for the particular size and vacuum of the tube employed, that it is i1nmaterial which terminals of the tube are connected to the conductors in and 17. in other words, as long as the high tension alternating electromotivc force is of a suliicient value to produce the brush discharge referred to and insuilicient to produce a disruptive arcing efi'ect within the tube, all of the high tension electromotive force waves ot'the sign tending to send the current from the cylinder 21 to the mirror 21 are effective in producing the brush discharge referred to, while all of the high tension electromotive force waves of the opposite sign are sup-- pressed, and this occurs irrespective of what the particular sign, that is whether positive or negative, of the effective and non-effective electromotive force waves may be. Furthermore, by using a polarized mill-ammeter in the secondary circuit, a reversal of the tube 15 in the secondary circuit was shown to reverse the direction of current flowing in the secondary circuit, and that for either con nection of the tube the amount of current flow was substantially the same and always uni-directional.

Our experiments further show that there is a considerable range between what may be called the critical values for any particular X-ray tube. For example, an X-ray high tension tube designed for use with a rectitying switch on voltages from 125,000 upward, may have a critical break-down value for the brush discharge from the cylinder 21 to the mirror 24 of about 80,000 and at about 105,000, to 110,000 volts, a second critical value is reached beyond which the voltage will produce a disruptive arcing dicharge which net only produces a comparatively while light in the tube which is totally unsuited for the production of X- rays, but .in addition rapidly disintegrates the target 22 and terminates thev usefulness of the tube. By operating the tubes with our system,'however,- the target and mirror show no appreciable wear, even after extensive use, since at no time is the current flowing through the tube of the disruptive or arcing variety.

Having established the uni-directional current flow through the tube as above described the cathode rays are reflected, of course, from the mirror 0.1 cathode 24 ins-t the target 22 and X-rays are geno upon the surface of the target and ejected from the tube, as indicated by the arrows producing practically a complete isphere of illumination in the tube.

in carrying out our invention We find it do: rable to use a transformer having a closed magnetic path, as indicated in Fi m t, although it will be understood that while other forms of transformers are notof as h an efficiency of operation as this type, ll they may be employed providing they are designed to deliver the proper value of I oriner shown in Fig. 4: consists in a pluality of hollow continuous rectangular punchings or stamping s 26 assembled together, and having Wound around one side thereof a primary winding 1, which. of course, is properly insulated from the core. The secondary winding consists preferably of a plurality of sections is, 14 and 14, each wound upon its own insulating spool or bobbin 27 27" and 27, these bobbins being of sulliciently large diameter to place the high tension secondary windings sufficiently remote from all metal parts of the trans former, so that no short circuiting of the secondary windings results. The openings in the rectangular stan'lpings are preferably of such a size that the circular spools or bobbins pass substantially through the center or" the openings, with sutlicient space around them so that there 1s no danger of arcing fronrthe winding of one section of the secondary coil to another section, or to the core. The stampings are preferably cut at one point. as indicated at 28, so that they may be inserted through the primary and sec ondary windings to facilitate assembling the transformer. 'llhese cuts are, of course, alternated as indicated in the stampings, or staggered in any desired manner so as to make the magnetic path of as low reluctance as possible. The transformer thus constructed is preferably immersed in a bath of oil, having a high insulating value.

in carrying out our invention we find it desirable to employ a controlling rheostat It in the primary circuit of the transformer 52,

so. that the electron'iotive force developed in the secondary winding of the transformer may 1' -adily be adjusted to the proper value between the two critical values referred to above for the particular Xuay tube being operated-so that the uni-directional current ilow above described may be secured through the secondary circuit of the transformer without the production of a disruptive discharge in the tube. It will also be understood that our invention is equally applicable to X-ray tubes in which an auxiliary anode 20 is employed, although in using such tubes we find it preferable to make no circuit connection to said auxiliary anode.

gh tension electromotive force. The trans-- It will be understood that our system Works equally Well Whether the tube 15 is provided with theauxiliary anode or not.

While we have shown our invention in the embodiment herein shown and described it will be understood that We do not limit ourselves to the particular arrangement or mechanisms shown and described, as We may employ any devices that Will produce a high tension alternating electromotive force of proper. value to be impressed upon the terminals of an X-ray tube to produce a resulting uni-directional current fioW therethrough without the use of extraneous devices for rectifying or modifying the alternating current. Each tube employed, of

'course, has 1tsown critical values of opera- 1. A system for operating X-ray tubes,

comprising the combination of a trans former having primary and secondary Windings, an X-ray tube having its terminals connected directly with the terminals of the secondary Winding of said transformer, and

means for controlling the operation of the transformer to produce an electromotive force in the secondary winding thereof of symmetrical wave form greater than that required to cause current to flow from the anode to the cathode of said tube, and less than that required to cause current to flow from the cathode to the anode of said tube.

2. In a system for operating X-ray tubes, the combination of a transformer having primary and secondary windings, a source of alternating current connected with the primary winding, an X-ray tube directly connected with the secondary Winding, and 111 *aus for producing in said secondary winding a potential of symmetrical wave form sutlicient only to cause a uni-directional current flow through said tube.

3. In a system for operating X-ray tubes, the combination of an X-ray tube, a closed high tension circuit directly connected with the terminals of said tube, and means for producing in said circuit an alternating electromotive force of symmetrical wave form'suflicient only in amount to produce a uni-directional current flow through said tube.

-l. in a system for operating X-ray tubes, the combination of a high tension X-ray tube having no'valve, a closed circuit directly connected With the terminals of said tube, and means for producing an alternating electromotive force of symmetrical wave form in said circuit, intermediate in value between the critical break-downvalues for the gap between the electrodes of said tube.

3. In a system for operating X-ray tubes, the combination ol a transformer having a closed magnetic circuit provided with primary and secondary windings, an X-ray tube having its terminals connected directly with the terminals of said secondary winding, and means for controlling the operation of said transl'ornicr to prmlucc an alternating electromolive force of symmetrical wave form in said secondary winding sullicient only to produce current flow in said tube from the anode to the cathode of said tube.

6. in a system for operating X-ray tubes, the combination of a valveless tube, a circuit directly connecting a source of altcrnating current with the terminals of said tube, means for producing in said circuit an alternating electromotive i'orce of symmetrical wave form sullicient only to produce a unidirectional current llow through said tube.

7. In a system for operating X-ray tubes, the coi'nbination of a transformer having primary and secondary windings, a source of alternating current connected in circuit with said primary winding, current controlling devices in said primary circuit, and an X-ray tube directly connected with the secondary Winding of said transformer, the amount of current flow through said primary circuit being proportioned to produce an electromotirc force of symmetrical wave form in said secondary circuit sullicient only to produce a uni-directional current flow through said tube.

8. The method of operating X -ray tubes Which consists in subjecting the terminals of a valvcless tube to an alternating electromotive force of symmetrical Wave form sulficient to produce current flow through the tube and insuiiicient to produce a disruptiw current flow through said tube.

9. The method of operating X-ray tubes which consists in subjecting the terminals of a vaiveless tube to an alternating electromotive force of symmetrical wave form of a Value between the critical breakdown values for the gap between the electrodes of said tube.

10. In a system of X-ray tube operation,

the combination of asource of alternating current of symmetrical'wave form, a trans former having primary and secondary Windings, an X-ray tube, connections between the source and said primary: winding, and connections between said secondary winding and the X-ray tube, whereby symmetrical current waves are delivered to said transformer and tube, the current waves of the secondary circuit being of a potential to produce current fiow through said tube with-- out disruptive discharge.

/ 11. in a system of X-ray tube operation, the combination of a source of alternating current of symmetrical wave form, a i'ormer having primary and secondary windings. an X-ray tube. and connections delivering symmetrical current waves to said primary winding and connections delivering synnnetrieal current waves from said secondary winding to said tube at a potential sullicient only to produce unidirectional cucrent flow through said tube,

12. in a,systcm of X-ray tube operation, the combination of a source of alternating current of substantially sine wave form, a transformer having primary and secondary windings, an X ray tube, and connections between said source and said transtorier and between said transformer and said tube for delivering to said transformer and said tube current waves of substantially sine form of a voltage sui'licient to produce current How and insulticient to produce disruptive discharge through said tube.

13. In a system of Xray tube operation, the combination of a source of alternating current ot substantially sine Wave form, a transformer having primary and secondary windings, a valveless X-ay tube, and con-- nections between said source and said transformer and between said transformer and said tube for delivering to said transformer and said tube current waves of bsantialiy sine form of a voltage sui'licient to groduce current flow and insuflicient to produce dis ruptive discharge through said tube.

14. The method of operating X-ray tubes which consists in impressing-upon the ter minals of the tube a symmetrical alternating elcctromotive force suiiicicntto produce current flow between the anode and cathode of the tube and of too low a -value to produce an alternating discharge between the elec' trodes of the tube.

In witness whereof, we hereunto subscribe our names this 11th day of April, A l 1914;

' GEORGE It. HGGAN...

HECTOR l hIAcLAGAN. Witnesses:

' ALBERT C. BELL, IRENE Fonnns'r. 

